Photographic fixing metoox



Patented Oct. 1 6, 1945 "UNITED STATE s PATENT OFFICE rno'rooasrmc FlXlNG METHOD James R. Alburger, Hollywood,'(lalli., assimor to Radio Corporation of America, a corporation or Delaware No Drawing. Original application Harbor to,

1939, Serial No. 306,971. Divided and t 331- plicatlon Qctober 8, 19.41, Serial No. 418,827

a or. one) 3 This invention relates to an improved photographic fixing bath, and more particularly to a fixing bath which is adapted for use'at abhor mally high temperatures and which can be used after the use 01' a hiahlyialkaline developer with= out causing reticulation.

The usual types of fixing baths are either practically neutral or are somewhat acid and include, in addition to the sodium thiosulphate, which dissolves the undeveloped silver salts, an acid sodium salt or similar acidifying agent and a hardening agent. If a film has been developed in a highly alkaline developer or has been developed at an unusually high temperature so that the gelatine is considerably softened and it is then placed in such a fixing bath, the sudden hardening of the surface accompanied by the acidifying thereof which causes a sudden con traction of the surface layer of the gelatine in relation to the lower layers has a tendency to cause reticulation. I find, however, that if the developed is placed in a dining both having an alkalinity approaching that of the developer, no such reticulation occurs and a correspondingly improved photographic image results.

- If an appropriate alkali is added to a sodium thlosulphate solution of ordinary concentration, it tends to soften the emulsion and render the film liable to damage in handling, and retlcu lotion is likely to occur when the :I-"w is placed in the succeeding wash. The addition of an ordinary harden agent to such a fixing bath does not prevent this difiiculty, since the softening of the gelatine occurs before the hardening agent has time to become efiective.

I secure the nemssary degree of alkalinity without the foregoing objections and with a hardening, instead of a softening of the gelatine by balancing thealkali with alum. The alum reacts with the alkali to first form aluminum hydroxide, which tends to be precipitated and to then form an aluminatewhich remains in solution,,but which has a hardening action on the gelatine. Ii. the alkali is used up by oxidation, or otherwise, a corresponding amount of aluminum 'hydromde is precipitated; thereby maintaining the alkalinity oithe bath constant.

One object oi the present invention is to provide an improvedmethod for fixing photographic emulsions.

Another object of the invention is to provide. a fixing method which may be. used atrelatively high temperatures. 1

Another obiectof the invention is to provide a method which will prevent reticulation iordeveloping motion picture film, by the carbon a fixing method which will the dissolved silver.-

oi the emulsion when either the developer or fixing bath is used at high temperatures.

Another object of the invention is to provide automatically recover Other and incidental objects oi the invention will be apparent to those smiled in the art from a reading of the following specification.

In my improved fixing method I use the usual sodium thiosulphate as a fixer, and I may also add paraiormaldehyde to the fixing bath as an additional hardener. The balancing of the alkali and alum may be accomplished as described and claimed in my U. S. Patents 2,199,903 and 2,193,- 904 of May 7, 1940, which descrlbesuch a balanced solution of alkali and alum applied to a developer where the alum acts as a bufier to the alkali.

This application is a division of my application Serial No. 306,71, illed November 30, 1939, Patent 2,321,347, in which my improved fixing bath itsell is claimed, a typical formula for which is. as follows:

Sodium thiosulphateulu; 400 Alum so-ee Sodium hydroxide. 30-20 Para-formaldehyde "grams" to Water cc 1000 The proportion of alum and sodium hydroxide 'is, as indicated above, in the general ratio of 4:3. The quantity of sodium hydroxide, however, is determined by the alkalinity of the de veloper which preceded the fixing bath. developer is highly alkaline, the g bath should have substantially the same alkalinity which can be determined as usual hy the. pH value. Since there is no change in the alkalinity of the solution in which the film is ersed,

there is then no tendency toward reticulation in passing the film from one solution to the other, while the hardening action of the fining bath is sufiicientto prevent any tendency toward reticulation when the him is immersedin the subsequent wash water. I

7 There is a tendency for the alkali in the fixing bath to be gradually converted to the'carbonate by the carbon dioxide in the air in contact with the surface thereof, and particularly when used dioxide in. the air carried into the bath by the film, and this reaction releases a corresponding amount of aluminum hydroxide from the solution or in other words the alum bufiers the alkali.

If the- This aluminum hydroxide settles out in the form 01' a gelatinous precipitate.

The fixing bath is alkaline and not acid, and it therefore does not suddenly stop the action or the developer in the emulsion, as would an acid fixing bath. The consequence of this is that any developer in the emulsion goes into solution in the fixing bath and reduces the dissolved silver in the fixing bath. This reduced silver, which is practically in colloidal form, is precipitated with the aluminum hydroxide and the 811-. ver may bereadily recovered from the resulting sludge. A further result of this action is that the fixing bath does not become saturated with silver salts and maintains its original activity over a relatively long time, If an insufilcient quantity of developer to accomplish the regeneration of the fixing bath is carried over by'the film, small additional quantities of developer may be added to the fixing bath for this purpose, and partly spent developer may be used, thereby recovering not only the silver in solution in the fixing bath, but also that in solution in the developer.

It will be apparent to those skilled in the art that the proportion of sodium thiosuiphate or hypo in the solution may be varied according to the requirements of the work at hand, and it will be also apparent that not only should the alkalinity be varied as pointed out, but that the quantity oiparaiormaldehyde should be varied according to the degree of hardening desired.- Ordinary formaldehyde may, of course, be added to the bath instead of the paraformaldehyde, but there is no point to such a procedure since the formaldehyde is converted into the paraiorxnaldehyde, and this procedure has the disadvantage that the hardening action varies according 'to the degree to which the polymerization has oc curred.

Iclaim as my invention:

1 a',sav,ooo

same as that 01 the alkaline developer in which the film was developed and an amount of alum sufilcient to bufier the alkali. 2. The photographic method including the steps of developing the emulsion including silver halide in an alkaline developer and thereafter fixing in a fixing hath having substantially the same alkalinity as the developer and an amount of alum sufiicient to butter the alkali.

3. The photographic method including the 1 steps oi developing the emulsionincludingsilver halide in an alkaline developer having a comparatively high alkalinity and thereafter fixing and hardening in a fixing bath having substantially the same alkalinity as the developer and an amount of alum suiflcient to bufier the alkali.

Q. The photographic method of treating an emulsion including silver halide which has been developed in an alkaline developer having a comparatively high alkalinity including fixing the emulsion in a fixing bath having substantially the same alkalinity as the developer and an amount of alum sufilcient to lender the alkali.

5. The photographic method of treating a silver halide emulsion which has been developed in a highly alkaline developer including the step oifixing and hardening the emulsion in a fixing bath having substantially the same alkalinity as the developer and an amount oi alum sufilcient to bufler the alkali.

6.' The method of preventihg reticulation oi .photographicemulsions including a silver hal- 1. The method of preventing reticulation of photographic emulsions including a silver halide, comprising the steps of fixing the image in, a

bath having an alkalinity substantially the i5 ide, comprising the steps of fixing the image in a fixing bath having an alkalinity substantially the same as that of the highly alkaline developer in which the film was developed and an amount of alum sufiicient to bufi'er the alkali.

i 7. The method of treating a photographic emulsion which includes a silver salt and has been developed in an alkaline developer, including the step of fixing the emulsion in a separate fixing bath which has (a) substantially the same alkalinity as the developer and (b) an amount of alum sufiicient to bufier the alkali.

JAMES R. ALBURGER. 

